ABSTRACT This proposal is designed to study the functional role of glucose sensing neurons in the ventromedial hypothalamus (VMH) in the regulation of energy homeostasis. Hormonal signals of energy sufficiency, leptin and insulin, regulate the activity of VMH glucose sensing neurons. Recent work from our laboratory suggest that leptin and insulin increase the glucose sensitivity of VMH glucose sensing neurons. Thus, under normal conditions leptin and insulin suppress the ability of VMH glucose sensing neurons to sense decreased glucose except when the brains glucose supply is threatened (e.g., hypoglycemia, fasting). Dysfunctional energy homeostasis in Type 2 diabetes mellitus (T2DM) is associated with central leptin and insulin resistance. The overall hypothesis in this proposal is that central leptin and insulin resistance during T2DM decreases the glucose sensitivity of VMH glucose sensing neurons. Decreased glucose sensitivity of glucose sensing neurons leads to an inappropriately enhanced response to decreased glucose during energy sufficiency. This results in a shift in energy homeostasis toward increased food intake and decreased energy expenditure which contributes to the progression of the disease. This hypothesis will be tested by 3 specific aims. Specific Aim 1 will investigate the cellular mechanism(s) by which leptin and insulin increase the glucose sensitivity of VMH glucose sensing neurons. Specific Aim 2 will determine whether glucose sensitivity of VMH glucose sensing neurons is decreased in T2DM and whether improving insulin resistance normalizes their glucose sensitivity. Specific Aim 3 will explore the role of the AMP activated protein kinase (AMPK)-nitric oxide (NO) signaling pathway in setting the "gain" for glucose sensitivity in glucose-inhibited (GI) neurons in health and T2DM. This novel pathway may provide a therapeutic target for normalizing glucose sensitivity during T2DM. While a number of studies have investigated the regulation of glucose sensing neurons, these are the first to provide a clear framework on which to understand the physiological role of these neurons and their contribution to the development of T2DM. Together, these studies will provide important information for the development of better therapies for T2DM.